1. Field of the Invention
The present invention relates to a method for forming a Cu-thin film on a semiconductor substrate such as an LSI substrate and more particularly to a method for forming a Cu-thin film on a semiconductor substrate using a dispersion containing Cu ultrafine particles individually dispersed therein.
2. Prior Art
In the recent semiconductor industries, the distributing wires formed on a substrate have been increasingly finer and the number of layers formed thereon has also been increased in proportion to the requirements for LSI's having a higher integration density and ability of operating at a high speed. However, this results in a decrease in the pitch of wires and in turn impairs the capacity between neighboring wires and the resistance of the wires and a problem accordingly arises such as delayed signal transmission. To eliminate this problem, it has been required to use a wiring material having a low specific resistance and an interlayer insulating film having a low dielectric constant. For this reason, attempts have been made to use, as a material for distributing wires, Cu having a low specific resistance and excellent resistance to electromigration (EM) in place of Al alloys or the like conventionally used. As a method for forming a Cu-thin film, there has been developed a so-called damascene method which comprises the steps of depositing a Cu film in, for instance, wiring grooves, via holes and contact holes according to, for instance, the sputtering method, CVD method or plating method and then subjecting the Cu film to a chemical-mechanical polishing (CMP) treatment.
However, such a conventional Cu-thin film-forming method suffers from the following problems. In the sputtering method among the methods for depositing Cu-thin films on a substrate, there is in general a limit in the degree of step coverage and further the reflow temperature should be reduced in order to ensure the compatibility with the method to the formation of a low dielectric film, even when the sputtering method is used in combination with the reflow method. For this reason, it is difficult to accelerate the embedding or filling up of fine grooves through reflow. Additionally, this method also suffers from a problem in that it requires a high processing cost. On the other hand, the plating method requires the formation of a Cu-thin film, as the so-called seed layer, on a barrier layer and this in turn results in such a problem that the plating liquid remains in voids. Both of the foregoing film-forming methods are insufficient for the method for forming the Cu-thin film. In addition, these methods are insufficient in the ability to embed or fill up, for instance, grooves for distributing wires when the aspect ratio of the grooves or the like is high.